RFR: 8150038: aarch64: make use of CBZ and CBNZ when comparing narrow pointer with zero

[Felix Yang]

Hi,

Please review the following webrev:
*http://cr.openjdk.java.net/~fyang/8150038/webrev.00/
<http://cr.openjdk.java.net/~fyang/8150038/webrev.00/>*

Jira issue: *https://bugs.openjdk.java.net/browse/JDK-8150038
<https://bugs.openjdk.java.net/browse/JDK-8150038>*

For several times I noticed the following pattern in C2 JIT code (the
java heap size is set to 200MB):


   2042   0x0000007f6c9419c4: ldr       w14, [x11,#32]  ;*getfield buffer
   2048   0x0000007f6c9419c8: cmp       w14, wzr
   2049   0x0000007f6c9419cc: b.eq      0x0000007f6c9425e4
;*invokevirtual reset

The two cmp and b.eq instructions can be combined into one "cbz" instruction.
Currently, the aarch64 port only makes use of CBZ and CBNZ when
comparing operands with Integer/Long/Pointer type with zero.

Patch fixes the issue by adding one similar combine pattern in the AD
file for Narrow pointer types(just like the sparc port does).

Tested with jtreg hotspot & langtools.  Is it OK?

Thanks,
Felix.
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